Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

Signs of marriage instability, such as parents contemplating divorce, when a child is just 9 months old are associated with problems falling and staying asleep when the child is 18 months old, said study researcher Anne Mannering, of Oregon State University. (Mannering was a research associate at the Oregon Social Learning Center at the time of the study).

"The quality of the parents' relationship can influence the quality of the parent-child relationship and vice versa," Mannering told MyHealthNewsDaily. "In addition, other research suggests that stress may negatively impact sleep, and we know that infancy is an important period for the development of sleep patterns."

It's possible that marital instability reflects stress within the family system, which may influence children’s sleep problems directly or through parenting, Mannering said. It's also possible that stress in the marital relationship could lead to parents being less responsive in their care to the child, she said, though more research is needed to determine this.

It's important to note that the study's measure of marital problems focused on the parents' thoughts of divorce, not level of conflict (severity of fighting), Mannering said. Future research will examine marital conflict more directly.

Researchers followed 350 families starting when the babies were 9 months old, and followed the families for nine months. All the children in the study were adopted to rule out the possibility of sleep problems due to shared genes.

Researchers found that the results held true even when taking into account difficult temperaments in the children, anxiety by the parents and birth order.